It is known in the packaging field to provide a continuous feed of articles, such as food product trays or containers, spaced at precise intervals in order to most efficiently accommodate interaction with a downstream processing station of the packaging line, such as a cartoner. This requirement often presents a problem due to the generally non-uniform supply of prepared products from upstream equipment. Inevitably, the processing equipment upstream provides surges with a greater number of containers being sent downstream in a short period of time. Conversely, the equipment sometimes lags behind due to intermittent downtime or other slowdown related intervals. This is most prevalent in the food preparation/packaging field where an even flow of prepared foods is difficult to maintain, especially where some manual intervention takes place.
In the past, others have provided a conveyor system for phasing and controlling the flow of closely spaced small articles, such as candy bars and the like, so that the articles can be fed in a controlled pattern to a wrapping machine. A typical system is shown in the U.S. Pat. No. to Bruno, 4,514,963 issued May 7, 1985. Insofar as we are aware of the prior state of the art equipment, the attempts of others to adapt this type of intelligent conveyor system to handling larger items, such as food entree trays, have not succeeded. Most systems of recent years in the article wrapping field using the teachings of the '963 patent involve a long series of phasing or indexing conveyors, each speed controlled by individual photocell sensors and an electronic controller. Even with this elaborate arrangement, it was not felt possible to reliably fill every carton on a cartoning machine, so no further efforts in this respect have been made. Also, an inherent shortcoming is that a surge or heavy backlog of articles coming into the system is still likely to end up producing a jam causing a shutdown of the packaging line. In most instances, this would result in damage to the product containers, leading to even more undesirable economic losses for the food processing plant.
In an attempt to alleviate the jamming problem, the owners/lessors of cartoning machines of the present assignee and others have, in the past, simply relied on mechanical indexing systems, coupled with running their machines at speeds of as much as 40-50% faster than the supply. Obviously this mode of operation is designed to simply avoid any upstream accumulation of the articles, and particularly to avoid the consequences of surging. Speeding up of the cartoning or other processing machine in this manner to in effect outrun the supply and thus accommodate the surges is not the best solution. In fact, this approach greatly compounds the problem of not being able to fill all of the cartons, thus reducing the overall efficiency of the packaging line.
Speeding up of the cartoning machine to accommodate surges in supply also introduces another problem; i.e. the increased speed makes a jam in the cartoning machine itself a greater possibility, and this in turn further reduces the operating efficiency of the packaging line. The cartoning machines or other processing machines on the line represent a significant capital investment to the owner/lessor, and thus machine efficiency, as well as longevity, is a major concern. As the speed of the cartoning machine is increased, the problem of premature component wear inevitably enters the picture and additional downtime of the packaging line can result. As downtime increases and the packaging line is not able to run, the lost production time mounts resulting in an obvious undesirable condition.
In this particular field, several conveyor systems with mechanical indexers have been produced, as mentioned above, and have met with some success. For example, U.S. Pat. No. 2,840,224 to Lefief, owned by the present assignee, discloses such an indexing conveyor assembly. Utilizing side running chains and staggered, rigid lugs containers on the line are able to be controlled successfully. However, because of the inherent nature of the arrangement, the speed is relatively slow. Also, there is no successful arrangement for providing controllable accumulation of containers in order to smooth out the feed supply between the peeks and valleys of the upstream operation. This prior arrangement of the '224 patent is typical of the best that has been available and which past practice indicates a need for running the cartoning machines at relatively high speeds. With the high speeds comes the increased possibility of jamming, as well as a greater probability of component wear and premature breakdown, all resulting in lower packaging line efficiency.
An alternative approach for this type of relatively reduced speed, mechanical indexing and transfer is shown in U.S. Pat. No. 3,543,911 to Brickson, also owned by the present assignee. In the system, since the containers are physically stopped and restatted by means of a flag stop interposed in the flow path of containers, an upper speed limit is quickly reached. The stopping and starting of articles tends to simply slow the packaging process too much to meet the demands of modern food processing lines.
Relatively recently, a general trend in the frozen, prepared food industry has been to move away from the flexible, aluminum foil trays to more sturdy plastic or paperboard (microwavable) trays, such as are used for food entree items. This change over has the potential for accelerating the move away from mechanical indexing arrangements to the more modern electronic phasing arrangements, similar to those that have been used with candy bars and other smaller items in the past. The paperboard trays are not as susceptible to interlocking during accumulation and can withstand close spacing or accumulation without damage. Being able to provide closely spaced, and even abutting articles of the paperboard trays has a potential of paving the way for moving away from the slower mechanical indexing systems of the prior art. This one factor of allowing a more constant supply of containers brings new thinking to the possibility of utilizing electronic controls of the type previously used in wrapping machines, as typified in the Bruno '963 patent, cited above.
A need therefore exists for a phasing conveyor system for providing a smooth, continuous flow of precisely spaced articles, such as microwavable food entree trays, for feeding a downstream cartoning machine or the like. Such a system would take advantage of the greater strength and more regular shape afforded by the paperboard containers now used in the food packaging field, and would be able to accommodate the faster food processing lines of today's technology.